JP-U-4-105906A shows a valve-timing controller which utilizes a motor torque. JP-11-324625A shows a valve lift controller which utilizes a motor torque. In these controllers, an electric power source of a driving circuit is turned ON from the time an engine-start signal is generated until an engine-stop signal is generated, otherwise the electric power source is turned OFF. A rotation sensor detects engine rotation speed to output an engine speed signal, on which a control circuit generates a control signal. The driving circuit supplies an electric current to the motor according to the control signal.
The engine continues to run by inertial force for a moment after the engine-stop signal is generated. At this time, the motor receives no electric current from the electric power source which the driving circuit operates. That is, the driving circuit supplies no electric current to the motor after the engine-stop signal is generated, so that the motor serves a load that generates a deviation in the valve opening/closing character. Thus, it is difficult to later realize a proper valve character required for starting the engine.
As described above, the driving circuit cannot supply the electric current to the motor before the engine-starting signal is generated. Thereby, if the valve opening/closing character is deviated before the engine-start signal is generated, the valve opening/closing character cannot be adjusted to the proper character for starting the engine.
The rotation sensor detecting engine rotation speed inherently has a lower-limit in which the rotation sensor can detects the lowest engine rotation speed, so that the rotation sensor outputs no engine speed signal for a moment after the engine is started. Until the engine speed signal is generated, the control circuit generates no control signal and the driving circuit conducts no activation of the motor. Thus, the motor again serves a load that generates a deviation in the valve opening/closing character, so that it is difficult to realize the proper valve character that is required for starting the engine.